Planar polycrystalline laser waveguides with the structure YAG/Yb:YAG/YAG were produced by ceramic processing. Transparent ceramics represent a valid alternative to single crystals as the flexibility of the ceramic process paves the way to new application opportunities. The implementation of different ceramic shaping techniques allows the production of complex or multicomponent (composite) structures that are generally difficult or about impossible to obtain with single crystals. A practical example are the planar structures presented here, characterized by a strict control of the dopant distribution obtained already during the shaping process, without further machining or bonding. The waveguides are composed of a laser active Yb:YAG layer obtained by tape casting with a thickness between 100 and 250 μm placed between dopant-free YAG cladding obtained by oxide powder mixing. The refractive index of Yb:YAG is higher than YAG thus realizing a multimode waveguide. Two types of geometries were tested: 1. simple planar waveguide with a sandwich structure (confinement in one direction); 2. waveguide with a rectangular cross section (confinement in two directions). The waveguides were tested for laser emission in a cavity end pumped by a fiber coupled diode laser, under quasi-CW pumping conditions (rectangular pump pulses with 10 ms duration, 10 Hz), delivering up to 60W at 936 nm. The planar waveguide has shown a maximum output power of 14.4 W (slope efficiency 39.1%, optical efficiency 27.4%) whereas the 2D waveguide had a maximum output power of 11.6 W (slope efficiency 38.4%, optical efficiency 22.4%). Lasing wavelength was 1030 nm.
We report a review on our recent developments in Yttebium and Neodymium doped laser ceramics, along two main research lines. The first is the design and development of Yb:YAG ceramics with non uniform doping distribution, for the management of thermo-mechanical stresses and for the mitigation of ASE: layered structures have been produced by solid state reactive sintering, using different forming processes (spray drying and cold press of the homogenized powders, tape cast of the slurry); samples have been characterized and compared to FEM analysis. The second is the investigation of Lutetium based ceramics (such as mixed garnets LuYAG and Lu2O3); this interest is mainly motivated by the favorable thermal properties of these hosts under high doping. We recently obtained for the first time high efficiency laser emission from Yb doped LuYAG ceramics. The investigation on sesquioxides has been focused on Nddoped Lu2O3 ceramics, fabricated with the Spark Plasma Sintering method (SPS). We recently achieved the first laser emission above 1 W from Nd doped Lu2O3 ceramics fabricated by SPS.
Yb:YAG ceramic solid-state laser gain media have been of growing interest for high-repetition rate and high-power lasers during the last few years. A great advantage of ceramic technology compared with that of single crystals is the flexibility of shaping methods allowing the production of near-net-shape components with a well-defined internal structure. A favorable dopant distribution can enhance laser efficiency by mitigating thermal effects. The presented work reports on Yb:YAG transparent ceramics composed of layers with different Yb doping produced by two different shaping methods: dry pressing of spray-dried powders and tape casting, all sintered under high vacuum. The selected geometry of materials was based on numerical simulations. Optical quality of produced ceramics was characterized and discussed in connection with the microstructure and laser emission results. Output power of nearly 7 W and slope efficiency of 58.1% were obtained in quasi-continuous wave regime from bilayered 0% to 10% Yb:YAG. In the case of multilayered materials, higher scattering losses were observed. The comparison of the two processing methods highlighted that the tape-cast materials provided higher optical uniformity and the diffusion zone between the single layers with different dopant content was about 150 μm compared to about 250 μm in samples produced by pressing of powders.
The use of Yb:YAG ceramic gain media in solid state lasers has been of growing interest for high repetition rate and high power lasers. Probably the most important advantage of ceramic production technology in comparison with that of single crystals is the flexibility of shaping methods that allow the production of near-net-shape components with a welldefined internal structure. In the case of Yb:YAG with dopant distribution designed accordingly to the pumping and cooling geometry the efficiency of the laser device can be enhanced by mitigating thermal lensing effects. The presented work reports on Yb:YAG transparent ceramics composed of layers with different Yb doping produced by two different shaping methods: dry pressing of spray-dried powders and tape casting, all sintered under high vacuum. The selected geometry of materials was based on numerical simulations. Microstructure of the produced materials was characterized by SEM and EDX with a particular attention to the dopant content across the layers. The optical quality of produced ceramics was characterized and discussed in connection with the microstructure and laser emission results. Output power of nearly 7 W and slope efficiency 58.1 % were obtained in QCW regime from bilayered 0-10 %Yb:YAG. In the case of multilayered materials higher scattering losses were observed. The comparison between the two processing methods highlighted that the tape-cast materials provided higher optical uniformity and the diffusion zone between the single layers with different dopant content was about 150 nm compared to about 250 nm in samples produced by pressing of powders.
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